The present invention relates to a procedure for manufacturing catalyst components to be used in polymerizing olefines. In particular the invention relates to the manufacturing of catalyst and carrier components having spherical shape, for olefin-polymerizing catalysts.
The use of Zieglar-Natta catalysts towards polymerizing olefines is known in the art. Such catalysts typically comprise a magnesium-based carrier substance which has been treated with a titanium halogen compound, and often also with an electron donor compound. Numerous methods have been worked out for manufacturing catalysts of this type, and a very great number of different compounds have been applied in order to modify said typical catalysts.
It is desirable in view of polymerizing that the catalysts have highest possible activity and thereby the required catalyst quantity is as small as possible. It is furthermore possible by the selection of catalyst to influence many other polymerization characteristics. Endeavours are frequently directed towards a result in which the products that are obtained would be in the form of even-sized, preferably spherical particles. This is reached, for instance, by the aid of using a catalyst carrier substance which occurs in the form of spherical particles of uniform quality.
Various methods are known in the art for producing carrier particles with spherical shape. In the so-called emulsion oil method, a melt of the carrier component is emulsified in a suitable oil, to be present therein in the form of spherical melt particles. The carrier particles in the emulsion are then shock-solidified by adding the emulsion into a cold hydrocarbon fluid, where the particles solidify. One of the drawbacks of this procedure is that preparing the carrier substance requires a component which is not useful in the later steps of catalyst manufacturing and which implies the existence of purifying and recirculation apparatus to this purpose. Another significant drawback is that this a charge process, in which the retention time is often prolonged, even up to several hours.
Another technique of the prior art for preparing particles of spherical shape for catalysts is the so-called spray drying method. For instance, in the GB Pat. No. 1,434,543 is disclosed a procedure wherein magnesium chloride is sprayed in molten state, or in aqueous solution, into hot air or nitrogen with the aid of a nozzle having such size that the particles which are formed will have the requisite particle size. In the U.S. Pat. No. 4,506,027, an equivalent procedure has been disclosed wherein ethanol and methanol solution of magnesium chloride is sprayed in droplet from into a hot nitrogen flow. The spray drying technique disclosed in these patents which have been described is based on the expedient that from the droplets produced in the nozzle, fluid is evaporated off with the aid of a hot, inert gas and as ultimate result solid carrier particles which are generally round in shape are obtained.
The spray drying method has some drawbacks which are partly associated wiht the quality of the carrier components obtained by the method and partly also with the process factors themselves. In spray drying, when a solvent is used, a change of the chemicals composition takes place all the time as solvent, to begin with, evaporates from the solution and, thereafter, from the surfaces of the solid carrier particles. As a consequence, the composition of the particles that are produced is not fully under control. The continuous evaporation of solvent from the particles causes growth of the particles' surface area and finally leads to particles which are porous and non-uniform in quality, containing varying amounts of solvent. Porosity detracts from the mechanical durability of the catalyst components and also impairs the activity of the catalyst that is obtained and its morphological properties. Another drawback is associated with the safety considerations of the process. Since the method is based on evaporating solvents, a consequence is that one has to handle great solvent quantities in gaseous form, and this involves a safety risk. Furthermore, comparatively high temperatures have to be used in the process, and this is not appropriate for all chemicals which are required.